There are many electronic products that use multiple digital audio channels. In particular, professional digital audio recording workstations come to mind. Today, high volume consumer electronic products such as desktop computers, laptop and notebook computers, tablet computers, and smart phones are being developed that also use multiple digital audio channels. In such products, digital microphone circuits are being used for improved noise immunity. In a digital microphone circuit, a relatively small (low complexity) integrated circuit, IC, interfaces with an otherwise analog sound pickup device (acoustic microphone), by converting an analog microphone signal into digital form and then transmitting the digital signal to a so-called “host” IC, such as an audio codec chip. In one case, a two-wire data bus arrangement is used to carry up to two audio channel signals of pulse density modulated audio data (from two separate microphones). The host IC supplies a clock signal on one of the wires, while the other wire carriers the data signal. The two microphone circuits take turns driving their data signal on the single, shared data line. More specifically, one of them drives its data signal while the clock is low, and the other drives while the clock is high. This is referred to as a time-division multiplexed data bus interface. The host IC detects the two channels of audio data as a function of the clock signal phase, and provides the detected microphone channels to any desired digital audio processing blocks, e.g. for signal enhancement. These audio channels may be part of for example a live audio or audio+video recording (e.g., streaming) session such as a conference call, where the two microphones may be used for improved sound capture quality (as compared to a single microphone).
There is a need for a relatively low cost and low power bus arrangement that can support substantially more than two digital microphone circuits, in a high volume consumer electronics product. One solution would be to simply add another bus data line, which can support an additional two microphones, and to continue adding an additional bus data line for each additional pair of microphones as needed. That, however, would increase the number of pins in the host IC that are to be dedicated for interfacing with such a bus. A more compact solution is desirable.